Factors influencing the clinical performance of x-ray systems both dental and medical are being modeled and evaluated in vitro using computer simulations and quantitative measurements derived from radiographic phantoms. Specifically included in this effort are measures of the variance associated with the radiographic assessment of file position in endodontically instrumented root canals using a variety of calibrated film-screen systems. The significance of the spectral composition of the x-ray beam, exposure a geometry, lesion size, and detector linearity also are being explored through measurement of associated image modulation, signal-to-noise ratio, transinformation and perceived lesion detectability. Preliminary findings suggest that endodontic determinations can be made reliably with significantly fewer noise equivalent quanta than conventionally used. Simulations also indicate that control of exposure geometry and detector sensitivity permit improved detection of small radiographic changes in dental lesions at greatly reduced x-ray doses (100x).